Atoms in Intense Fields

周祥顺

台湾海洋大学光电科学研究所

2013年7月8日

四川大学

Contents

• Introduction • The dressed-atom approach• The dressed-atom multiphoton spectroscopy• Conclusions• Outlook

I. Introduction

• Subject: The behaviors of atoms in intense laser fields.

• Methods: Dressed-atom approach• Example: Pump-probe spectroscopy

Pump-probe spectroscopy

The modification of the absorption spectra of theprobe beam due to the presence of the coupling beam.

half-wave plate

polarizer

polarization beamsplitter

photodiode

half-wave plate

II. The dressed-atom approach

Step 1: Consider only the system “ atom + coupling photons interacting together” . Step 2: Consider the coupling with the vacuum or the probe photons.

Total Hamiltonian:

Atomic Hamiltonian :

: Laser Hamiltonian

Interacting Hamiltonian :

ALLA HHHH

AH

LH

ALH

Two-level systems• Two-level atoms in the presence of a

single-mode radiation field

12A

H g g

12A

H e e

: Atomic frequency : Laser frequency

nnnH LL )21(

L

Uncoupled states (bare states)

,I g n

Uncoupled Hamiltonian：

Uncoupled states： ， , 1F e n

with

with

As ，0

:detuning

LA HHH 0

LIF EE

LI nE 21

LF nE )1(21

IEIH I0

FEFH F0

)21( nEE IF

Coupled states (dressed states)H E Dressed states：

Rabi frequency ：

( 0) 1 1( ) ( )2 2E n n

1,,2

1, nengn

2 q n

with nqngHne AL ,1,

Ladder of energy levels

2

2

2

,g n , 1e n

,n

,n

, 1n

, 1n

, 1g n ,e n 2

Bare states Dressed states： ：

L

III. Dressed-atom multiphoton spectroscopy

• In the first step, the coupled system “atoms + coupling photons” is described by the dressed-state wave functions which describe the coupling field to all orders.

• In the second step, we use perturbation theory to treat the probe field.

• Quantum interference arises naturally in the dressed-atom multiphoton spectroscopy.

Ref. H. S. Chou and Jörg Evers, Phys. Rev. Lett. 213602 (2010).

Anomalous electromagnetically induced absorption (EIA)

• EIA

probe-coupling detuning (MHz)

The absorption of the probe beam is substantially enhanced when copropagating orthogonally polarized probe and coupling beams interact with a degenerate two-level system. Ref. A. M. Akulshin et. al. , Phys. Rev. A57, 2996 (1998).

:coupling beam:probe beam

Lezama’s condition for EIA1e gF F

em

Ref.：A. Lezama et al, Phys. Rev. A59, 4732 (1999).

： 2 1 0 1 2

1 0 1gm ：

Spontaneous coherence transfer (SCT)

EIA is caused by the spontaneous transfer of thelight-induced Zeeman coherence from the excitedlevel to the ground level.Ref.：A. V. Taichenachev et al, JETP Lett. 69 819 (1999).

:coupling beam :probe beam :SCT

1 0 1

1 0 1 22em ：

gm ：

Interpretations of Lezama’s condition

The excited-state coherences are very small forsystems with and ,because thepopulations are trapped in the lower levels. SCTand EIA can not take place for such systems.

1 0 1

1 0 1

1 0 1 22

0 11

1e gF F e gF F(I): (II):

1e gF F e gF F

: populations

Anomalous EIA• Transition in the line of 3 2g eF F 85Rb1D

Ref.：S. K. Kim et al, Phys. Rev. A68, 063813 (2003).Probe frequency p

Abs

orpt

ion

(ii) Intermediate coupling intensity

(i) Low coupling intensity

12 3 (EIA)

4 5

(iii) High coupling intensity

1e gF F

Anomalous EIA • Transition in the line of 1 1g eF F 87Rb1D

Ref.：S. K. Kim et al, Phys. Rev. A68, 063813 (2003).Probe frequency p

Abs

orpt

ion

123(EIA)

(i) Low coupling intensity

(ii) Intermediate coupling intensity

(iii) High coupling intensity

e gF F

4(EIA)

5(EIA)

Anomalous EIA

• Transitions and in the line of

2 2g eF F 87Rb1D

Ref.：S. K. Kim et al, Phys. Rev. A68, 063813 (2003).

e gF F

The anomalous EIA peak breaks up again at intermediate coupling intensity.

3 3g eF F

Anomalous EIA 3 2g eF F

0 1 2

3 2 1 0 1 2 3

(I) Bare-atom picture

:coupling beam:probe beam

2 , 2n

2 , 2n

1 , 2n

1 , 2n

1 , 2n

0 , 2n

0 , 2n

1 , 2n

2 , 2n

2 , 2n 3, 3n 3, 3n

0 , 1n

0 , 1n 1 , 1n

1 , 1n 2 , 1n

2 , 1n 3, 2n

1 , 1n

1 , 1n

2 , 1n

2 , 1n 3, 2n

0 , n

0 , n

1 , n

1 , n

2 , n

2 , n3, 1n

1 , n

1 , n

2 , n

2 , n 3, 1n

(II) Dressed-atom picture

1 2

14p

14p

12

0

22p

22p

Ref. H. S. Chou and Jörg Evers, Phys. Rev. Lett. 213602 (2010).

Anomalous EIA

0, 2n

0, 3n

0 ,n0, 1n

0 , 1n

0 , 2n

1 ,n

1 ,n 1 , 1n

1 , 1n

1 , 2n

1 , 2n 1 , 2n

1 , 2n

1 , 1n

1 , 1n

1 ,n

1 ,n

1 1

1 1g eF F

1 0 1

1 0 1

(I) Bare-atom picture (II) Dressed-atom picture

p

12p

12p

Anomalous EIA

0, 2n

0, 3n

0 ,n0, 1n

0 , 1n

0 , 2n

1 ,n

1 ,n

1 , 1n

1 , 1n 1 , 2n

1 , 2n 1 , 2n

1 , 2n

1 , 1n

1 , 1n

1 ,n

1 ,n

1 1

2 2g eF F

p

2 ,n

2 ,n

2 , 1n

2 , 1n

2 , 2n

2 , 2n

2 ,n

2 ,n

2 , 1n

2 , 1n

2 , 2n

2 , 2n

2 2

24p

24p

IV. Conclusions

• We propose the dressed-atom multiphoton spectroscopy (DAMS) to interpret the nonlinear pump-probe spectra.

• We apply the DAMS to provide a clear physical interpretation for the anomalous EIA.

V. Outlook

• Nonlinear pump-probe spectroscopy.• Quantum control via interference and

coherence• Relativistic many-body theory of laser-

dressed atoms

Thank you for your attention.

Atoms in Intense FieldsContents投影片編號 3投影片編號 4II. The dressed-atom approach投影片編號 6投影片編號 7投影片編號 8Coupled states (dressed states)Ladder of energy levels 投影片編號 11投影片編號 12Lezama’s condition for EIA 投影片編號 14投影片編號 15投影片編號 16投影片編號 17投影片編號 18投影片編號 19投影片編號 20投影片編號 21IV. ConclusionsV. Outlook投影片編號 24